user can't make new snapshot until previous snapshot is saving

* xlog/snapshot file format iterator object added (tnt_log)
* tnt_snapshot stream created
* refactored tnt_xlog and tnt_stream streams to use the same tnt_log object
* storage iterator added (for fetching tuples from snapshot or other
tuple storage)
* console client refactored to support snapshot files (cat command)
(this also fix for https://bugs.launchpad.net/tarantool/+bug/1028475)
* snapshot test case added

daemon can watch box.info.snapshotting variable do stop its loop temporary

A fix and a test case for Bug#0152018
"panic_on_wal_error doens't work for duplicate key errors"

Add a check for panic_if_error after invocation
of row handler, in addition to the log io cursor
checks.

(https://bugs.launchpad.net/tarantool/+bug/1050951)

A fix and a test case for Bug#1051006
"Tree iterators return garbage if an index is modified between calls"

Mark in a deleted node in sptree.h that it's been  put into the
garbage heap. When iterting over a garbage collected node, skip it,
and go up the stack until we find the first valid node.

This breaks the "sorted" quality of tree iterators in case there
are modifications between invocations of an iterator:
it is possible that a node is deleted and recycled, and we don't see
it in the iterator. When we go up the stack, we can jump to a different
part of the range than the one the recycled node belongs to.
. With this fix, it is also possible, that the iteration goes more
than once over entire tree range. But it's a good enough quick fix for a
crashing expire loop, which uses the tree iterator over the primary key to
scan the entire range and deletes expired keys on the go (additionally,
deletions may occur between invocations of the expire loop).

Bug#1046260 CentOS builds: "no debugging symbols found"
Do not strip the binary in rpmbuild.

See http://public.kitware.com/Bug/view.php?id=7435

Fix a race condition between build of bundled luajit and build of
tarantool_lua_info.h.

(Failure to build tarantool_lua_info.m on Debian SID).

Test what happens when we exhaust slab allocator memory.

Output year-month-day hour:min:sec.ms in the log.
Take pid into square brackets for better visibility.

fiber_setcancelstate(true) in admin fiber is no longer
necessary and can lead to bugs, if admin fiber works
with wal writer queue.

Conflicts:
	src/CMakeLists.txt
	src/admin.m
	src/tarantool_lua.m
	test/box/lua.result

Move print_stat to admin.rl
Make tarantool_lua_stat.m a bit simpler.
Restore the original formatting of show stat.
Fix a bug when rps and total were reversed
in the new show stat output.

Conflicts:
	doc/user/stored-procedures.xml
	src/CMakeLists.txt
	src/tarantool_lua.m
	test/box/lua.result

Make names a bit more consistent, add comments,
fix style.

Conflicts:
	mod/box/box_lua.m
	test/box/lua.result